Problem: Solve for $x$ and $y$ using substitution. ${-x-2y = 1}$ ${x = -3y+1}$
Explanation: Since $x$ has already been solved for, substitute $-3y+1$ for $x$ in the first equation. ${-}{(-3y+1)}{- 2y = 1}$ Simplify and solve for $y$ $3y-1 - 2y = 1$ $y-1 = 1$ $y-1{+1} = 1{+1}$ ${y = 2}$ Now that you know ${y = 2}$ , plug it back into $\thinspace {x = -3y+1}\thinspace$ to find $x$ ${x = -3}{(2)}{ + 1}$ $x = -6 + 1$ ${x = -5}$ You can also plug ${y = 2}$ into $\thinspace {-x-2y = 1}\thinspace$ and get the same answer for $x$ : ${-x - 2}{(2)}{= 1}$ ${x = -5}$